Spuddle, a 12 day LP is not a problem. Usual range is between 11 and 16 days - 14 days is considered average. You need to be sure when you O to have an accurate indication of O. A twinge alone is not enough - sorry - a twinge could be anything.
Have you tried observing CM? That usually gives a good indication of O. You could also try OPKs - but they don't necessarily work for everyone!
A LP less than 11 days, ie 10 days or under, could signal a problem and should be checked.
HTH
TICKLISH